Over the past few decades, display technologies have witnessed significant technological advancements that allow for realistic two-dimensional imaging, as well as three-dimensional imaging. Generally, this can be achieved by stereoscopic-type display systems employing two-dimensional screens (such as liquid crystal displays, light-emitting diode-based displays, and the like) for recreating perceivably three-dimensional images, by utilizing binocular disparity. In such a case, different two-dimensional views of a given three-dimensional object/scene are rendered upon (i) separate two-dimensional displays for right and left eyes of a viewer, or (ii) a single two-dimensional display that is typically shared in a time multiplexed or polarization multiplexed manner for both the right and left eyes of the viewer. When such different two-dimensional views are combined in the viewer's brain, the viewer perceives depth of the given three-dimensional object/scene.
However, there exist limitations associated with the use of two-dimensional displays for three-dimensional imaging. Firstly, using binocular disparity for perceiving depth leads to vergence-accommodation conflict. Secondly, such two-dimensional displays are often implemented in head-mounted devices (such as virtual reality devices, augmented reality devices, and the like), and prolonged use of such head-mounted devices leads to discomfort and eye fatigue for the viewer. Therefore, nowadays, developments are being made to display three-dimensional objects/scenes upon three-dimensional displays.
Presently, the display systems employ autostereoscopic displays in order to overcome the aforesaid limitations of two-dimensional displays for three-dimensional imaging purposes. Autostereoscopic displays are of various types that include, but are not limited to, multiview-type displays, holography-type displays and volumetric-type displays. The multiview-type displays typically recreate multiple views of the given three-dimensional object/scene as observable from different positions by employing, for example, parallax barriers. However, such multiview-type displays suffer from issues such as abrupt changes within views, reduced light intensity and lower imaging resolution. The holography-type displays typically capture light field emanating from the given three-dimensional object/scene by registering amplitude, wavelength and phase information, and reproducing the given three-dimensional object/scene using coherent light. However, such holography-type displays require significant computational resources and dynamically variable spatial light modulators (SLMs) with very high resolution, which currently are not available, thus limiting the visual presentation attainable by true holographic-type display systems.
The volumetric-type displays typically employ projection equipment for projecting light in a three-dimensional volume, active light-emitting voxels, or optically active media, to create a three-dimensional image of the given three-dimensional object/scene. However, there are a number of limitations associated with the display systems employing conventional volumetric-type displays such as difficulty in scalability, computationally intensive data processing, and the like. Specifically, such conventional volumetric-type displays are often bulky and have substantially large dimensions. Furthermore, in volumetric display technologies utilizing image projection, noticeable differences of image magnification are generally associated with the three-dimensional image displayed via such volumetric-type displays. In other words, the viewer is often able to perceive substantial change in magnification within the displayed three-dimensional image.
Further a volumetric display device utilizing a rear image projection in conjunction with discretized and selectively addressable light diffusing projection surfaces of the projection volume can be substantially large and bulky. A major reason attributing to the bulkiness of the system is a considerably long optical path of the modulated light from the image projector (spatial light modulator) to the projection volume (for example, rear light diffusing surface which is the closest to the spatial light modulator). A typical length of such optical path can be for example 2 meters or 1.5 meters. To reduce the linear size of the device, the optical path could be folded by utilization of plane mirrors. Nevertheless, utilization of multiple reflecting surfaces, reduces the overall light intensity hitting the projection volume thus reducing the image brightness and contrast. Moreover, often practical number of flat mirrors for the folding of optical path might not result in considerably small form-factor of such volumetric display device.
One of ways how to reduce the overall optical path is to utilize a short-throw or ultra short-throw image projector. Such image projector achieves great image magnification at considerably short distances and thus is being characterized by a high throw-ratio. Typically, this is being achieved by utilization of wide-angle or ultra wide-angle projection lenses. In the context of volumetric display, utilization of such wide-angle projection lens would result in a considerable change of image magnification throughout the projection volume (individual image planes associated with the volumetric 3D image). Subsequently, this results in an aberrant representation of three dimensional (3D) objects and scenes, as the different parts of the 3D image have varying magnification. Although by a much subtle amount, a varying image magnification is a problem occurring also in long focal-length projection lenses originally utilized in the image projection subsystem of the volumetric display systems.
Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with existing display systems for three-dimensional imaging.